AN AMBISONICS FORMAT FOR FLEXIBLE PLAYBACK LAYOUTS
Hannes Pomberger, Franz Zotter · 2009
Abstract: Ambisonics represents the sound field as a sum of angular modes (circular/spherical harmonics). The Ambison-ics signals representing these angular modes are usually decoded to a set of loudspeakers by mode-matching equations. This works if the speakers are well-distributed on a circle or sphere. But Ambisonics playback arrangements frequently do not cover an entire circle or sphere due to practical constraints, which leads to non-trivial problems in decoder design. This paper presents two approaches to extend the capacities of Ambisonics to partial circular or spherical layouts by enabling decoder-design with mode-matching. The first approach selects suitable sets of harmonics, based on their sym-metry and periodicity, and works for some particular partial layouts. But these selections are difficult to use for playback on default loudspeaker layouts, i.e. a full circle/sphere, and are not applicable to arbitrary partial layouts. So finally, the paper presents a second approach, which provides full flexibility of partial layouts, while enabling playback on full default layouts. This favored second approach is driven by a reduced set of signals, which can be utilized to optimize the requirements for storage and transmission. The authors propose to store and transmit the reduced set of signals within a file exchange format that includes an appropriate reconstruction matrix. Key words: Ambisonics, playback on partial domains. 1